Our body is prone to many infections and illnesses. While certain respiratory bacterial and viral infections have longer repercussions compared to some mild anomalies that wither away with medical treatment, some chronic lung infections cause fluid to accumulate in the space between the lung and the rib cage.

Found in the thin space between the lungs and the tissue covering the lungs called pleural space, this occurrence is called pleural effusion. Normally detected through a chest X-ray, pleural fluid sample testing is a process that involves removing a sample of this fluid using a laboratory method. The fluid is obtained by inserting a needle into the pleural space known as thoracentesis. The testing is used to diagnose the precise cause of an abnormal build-up of this thick fluid. Thoracentesis is important because it enables doctors to understand what caused the fluid to collect in the lungs and how to treat the problem and corresponding anomalies.

Also Read: Pleural Effusion: Causes, Symptoms And Treatment

Purpose Of Thoracentesis

Performed in a hospital, or outpatient clinic, the purpose of testing pleural fluid is to determine the cause of a pleural effusion. Pleural fluid testing plays an important role in diagnosing the reason why a pleural effusion has occurred.  When thoracentesis is done for pleural fluid testing, it is called diagnostic thoracentesis. If the procedure is done to reduce fluid build-up and relieve symptoms, it is called therapeutic thoracentesis. Many health conditions can cause a pleural effusion and identifying the underlying can help guide treatment. The procedure to obtain a sample of pleural fluid involves inserting a thin needle into the pleural space to withdraw a small amount of fluid.

What Does Test Measure?

Pleural fluid testing may involve multiple different analyses and measurements. Some of them include:

Visual And Odour: Pleural fluid analysis with the naked eye and smell will help detect abnormalities in its colour, texture, and viscosity.

Bacteria And Fungi: Through a technique called a gram stain that applies a chemical dye to the slide, a pleural fluid sample is placed on a laboratory slide to find out the kinds of cells, germs like bacteria, or fungi causing infections.

Cytology: Cytology is a detailed examination of the specific kinds of cells in the sample and is often utilized to determine whether cancer cells are present in the pleural fluid that may be the cause of pleurisy or other problems

Bacterial or Fungal Culture: A culture test places a sample of the pleural fluid that is left for a period of a few days to see if any bacteria or fungi grow.

Acidity Analysis: This measurement assesses the acidity, or pH, of the pleural fluid.

Cell Count: This analysis determines the total number of cells in the sample and can also include a cell count differential, which calculates the amounts of each cell type present.

Total Protein Count: Total protein is the sum of all types of proteins in the pleural fluid and may be reported as the concentration of protein in the sample.

Lactate Dehydrogenase: LDH or lactate dehydrogenase is a type of enzyme tested via this sampling. It may be produced at higher levels in response to chronic inflammation or tissue damage.

When Is Thoracentesis Advised?

Pleural fluid testing is advised after an X-ray, CT scan, or ultrasound shows a large build-up of fluid in the pleural space. The symptoms of pleural effusion are chest pain, shortness of breath, chronic cough, chest infection and respiratory distress. While thoracentesis is advised for most patients, people with co-morbid conditions, such as serious lung disease, or a skin infection around where the needle would be inserted are not recommended to go for this sampling.

Test Procedure

No preparation is required for thoracentesis, but the doctor must be informed about any medication, especially about blood-thinning drugs. A local anaesthetic is applied after which a needle is inserted into the pleural space surrounding the lung to withdraw fluid through the needle. In some cases of large pleural effusion, the physician may put a thin tube called a catheter in place once the fluid for testing is removed to drain excess fluid over several hours or days.

Test Results

Results of thoracentesis play a vital role in interpreting the pleural fluid test.  Despite a useful diagnostic tool, this sample testing alone cannot always identify the cause of a pleural effusion.  Testing can also look for other underlying causes of a pleural effusion may also be advised to look for evidence of conditions like infection, empyema, and some types of cancers such as breast cancer, lung cancer, lymphoma, and ovarian cancer.

Risks Of Thoracentesis

Thoracentesis rarely causes serious side effects or complications; however, some potential risks may include:

Punctured Lung:  A condition known as pneumothorax, if the needle pierces the lung, it can cause air to build up in the pleural space leading to a collapsed lung.

Bleeding:  A uncommon complication is bleeding from the procedure that causes the build-up of blood in or near the lung. This blood needs to be drained on an urgent basis.

Infection: Though a rare occurrence, it is possible for an infection to occur from the needle puncture.

Punctured liver or spleen: Performing thoracentesis with ultrasound while you are sitting up makes this complication unlikely to happen, yet this may happen if the needle pierces the liver or spleen during the procedure.